User Manual

Sequence of Operation
Gas Furnace (Optional)
14
Siemens Industry, Inc.
Application Note, App 14900
140-1231
2020-02-11
● An Inter-stage Delay (StgDlyHt) timer must be enforced between the third heating
stage OFF and the second heating stage OFF to ensure that the second heating
stage won’t be turned off until the third heating stage has been turned off for the
time set in Inter-stage Delay timer.
If HeatStg = 3, the application controls HTG STG 3 (O/B) as follows:
● If IndoorTmpEff is less than the switching on point of the third heating stage
(HeatingSp – 1/2 HeatingDB- StgDifHt*2), the third heating stage has been OFF
for at least the time set in MIN OFF, and Inter-stage Delay timer has expired, HTG
STG 3 (O/B) is turned ON.
● If IndoorTmpEff is greater than the switching off point of the third heating stage
(HeatingSp + 1/2 HeatingDB – StgDifHt*2), and the third heating stage has been
ON for at least the time set in MIN ON, HTG STG 3 is turned OFF.
Gas Furnace (Optional)
When the HVAC Mode is in heating mode, and the heating staging logic controls a
furnace, Parameter P105 (HTG FAN) FanOpr in the Installer Setup Menu must be set
to gAS.
If a heating stage has been ON, it will not shut OFF until its minimum ON timer has
expired. Likewise, if a heating stage has been OFF, it will not turn ON until its minimum
OFF timer has expired.
In addition to above rules, a time-based separation of heating stages--Heating Inter-
stage Delay--applies to the unit with multiple heating stages.
The following paragraphs explain the electric heater staging.
If HeatStg = 0, the application does not control HTG STG 1.
If HeatStg ≥ 1, the application controls HTG STG 1 as follows:
● If IndoorTempEff is less than the switching on point of the first heating stage
(HeatingSp – 1/2 HTG DB), and the first heating stage has been OFF for at least
the time set in MIN OFF, HTG STG 1 (W1) is turned ON.
● If IndoorTempEff is greater than the switching off point of the first heating stage
(HeatingSp + 1/2 HeatingDB), and the first heating stage has been ON for at least
the time set in MIN ON, HTG STG 1 (W1) is turned OFF.
If HeatStg ≤ 1, the application does not control HTG STG 2 (W2).
If HeatStg ≥ 2, the application controls HTG STG 2 (W2) as follows:
● If IndoorTempEff is less than the switching on point of the second heating stage
(HeatingSp – 1/2 HeatingDB - StgDifHt), the second heating stage has been OFF
for at least the time set in MIN OFF, and the Inter-stage Delay timer has expired,
HTG STG 2 (W2) is turned ON.
● If IndoorTempEff is greater than the switching off point of the second heating
stage (HeatingSp + 1/2 HeatingDB – StgDifHt), and the second heating stage
has been ON for at least the time set in MIN ON, HTG STG 2 (W2) is turned OFF.
● An Inter-stage Delay (StgDlyHt) timer must be enforced between the third heating
stage OFF and the second heating stage OFF to ensure that the second heating
stage won’t be turned off until the third heating stage has been turned off for the
time set in the Inter-stage Delay (StgDlyHt).